The biological activity of copper is to a large part due to its ability to exist in what is termed the “free” state as metallic copper or “ionic” state as a copper salt or oxide. While copper is almost always combined with other elements or minerals, under certain conditions copper can exist in the ionic or free copper state, both of which are biologically active and thus gives copper the ability to kill bacteria, viruses and fungi.
Copper and its salts and oxides, have been used since antiquity to treat a wide variety of ailments and injuries. The earliest recorded medical use of copper is found in an Egyptian medical text known as the Smith Papyrus, written between 2600 and 2200 B.C., which describes using copper to sterilize chest wounds and drinking water. Other early texts such as the Ebers Papyrus (written around 1500 B.C.), De Materia Medica by Dioscrides, De Medicina by Aulus Cornelius Celsus at the time of the first Roman emperors, and works Pliny and Hippocrates also describe the medicinal use of copper, in metallic form or as a salt or oxide. The materials mentioned in the early texts include copper carbonate (probably as the mineral malachite), copper chloride that was formed by the action of salt water on metallic copper, verdigris that is formed by the action of hot vinegar (acetic acid) vapors on metallic copper, and blue vitrol which is copper sulfate. Copper, in metallic form or as a salt or oxide, was used to treat burn wounds, itching headaches, trembling limbs, boils and other maladies as bloodshot eyes, inflamed or bloodshot eyes, cataracts, “fat in the eyes” (possibly trachoma), and cataracts. The Greeks treated wounds with a dry powdered mixture of copper oxide and copper sulfate and also a boiled mixture of red copper oxide (cuprous oxide, Cu2O) and honey. Black copper oxide mixed with honey was used to remove intestinal worms and, in diluted form, was also used to clear the head by administrations as nose drops, as a stomach purge when drunk as a honey and water mixture, used as eye drops to remove pain, and as a rinse for canker sores. In the Americas the Aztecs treated sore throat by gargling with a mixture copper and other ingredients. In India copper was used to treat lung diseases and in ancient Persia powdered copper carbonate was sprinkled on boils, and copper acetate and copper oxide were used for diseases of the eye. In addition, for many centuries it was known that water could be transported in copper containers with little or no slime formation. When wooden or clay water vessels were used as a water carrier a copper coin or bar was placed in the vessel for the same purpose, this particular practice being widely used by those traveling across the American West in the 1800s.
With the discovery of the existence of microbes in the 1800s, the antimicrobial properties of copper and its compounds became more widely investigated, and these investigations continue to the present day. A few examples of the literature are articles by J.O Noyce et al, “Inactivation of influenza A virus on copper versus stainless steel surfaces,” Applied Environmental Microbiology, Vol. 73 (2007), pages 2748-2750; J.L. Sagripanti et al. Mechanism of copper-mediated inactivation of herpes virus,” Antimicrob Agents Chemotherapy Vol. 41 (1997), pages 8122-817; G. Borkow et al, “Copper as a biocidal tool,” Current Med. Chem. Vol. 12 (2005), pages 2163-2175; U.S. Patent Application Publication No. 2001-0221307 (antiviral agents, antiviral fibers and antiviral fiber structures; U.S. Pat. No. 7,192,602 for Walter-insoluble, antimicrobial silicate glass and use thereof; and L. Esteban-Tejeda et al, “Antibacterial and antifungal activity of a soda-lime glass containing copper nanoparticles,” Nanotechnology, Vol. 20 (2009) 505701 (6 pages).
Although there is mention of copper, Cu0, and cupric ions, Cu+2, as an antimicrobial agents in various forms and applications, for the most part it consists of generalized comments without a real description of the specific nature of how the copper species was employed (see references below); for example, as a film, solution, particle etc. See G. Borkow et al, Copper as a biocidal tool,” Current Med. Chem. Vol. 12 (2005); pages 2163-2175; N. Yamamoto et al, Biochem. Biophys. Acta. 2001, 91, 257; F.T. Jordan et al, Vet. Rec. 1971, 89, 609; and A Totsuka, et al, Jpn. J. Microbiol. 1974, 18, 107. In addition, there are only a few references that mention that the effect of the oxidation of Cu0 to CuO is a lessening the antimicrobial action of the substrate. The oxidation of Cu0 to CuO is well known and is typically prevented by use of a protective film coating that is placed on top of a Cu0 layer. However, in addition to protecting the Cu0 surface from oxidation, for antibacterial or antimicrobial uses, the coating must be one that will not inhibit the antimicrobial or antimicrobial activity of the article. Stated another way, the protective film has to be effective is protecting the surface from oxidation while maintaining antibacterial or antimicrobial action. No mention has been made of the use of cuprous oxide, Cu2O, particularly Cu2O nanoparticles, as an antimicrobial agent in or on glass. Further, no mention was made in the articles of having a protective coating over the copper nanoparticles that would serve to diminish or slow down the degradation of the nanoparticles' antibacterial or antimicrobial activity.
In the last twenty to thirty years touch screen devices have become prevalent in society, first appearing on automatic teller machines and later on vending machines, cell phone, computers, personal electronic devices, and more. With the higher concentrations of people in cities, along with the high mobility throughout the world, there has been rising concern about the transmittal of microbes. While microbes can be removed or killed by the proper cleaning of surfaces using an appropriate biocide, this is often not truly practical solution because many persons can use a given device in a short time period and device cannot be continually cleaned. Consequently, it is highly desirable to have surfaces that are durable and also possess antimicrobial properties that last over a period of time before they are cleaned so that different persons using a device are equally protected. Embodiments are directed to this end.